Polarized hull plating was a defensive hull technology used on starships. Before the development of deflector shielding, hull polarization was the primary defensive measure for starships against enemy weaponry.
History
In the 22nd century, this technology was used on Earth starships such as the J-class and the Template:ShipClass and on smaller auxiliary vessels such as the shuttlepods. During the months the Enterprise was in the Delphic Expanse, polarization technology on Earth had been improved by 12%. (Star Trek: Enterprise; ENT: "Horizon", "Vanishing Point", "Home")
In the 24th century, starships still occasionally polarized their hull plating, though not typically as a defensive countermeasure. One example was disrupting an enemy's tractor beam by rotating the frequency of the hull plating's electromagnetic field. Ships also sometimes polarized their hull plating to help mask their sensory signature, which worked by interfering with the enemy's sensors. (DS9: "In Purgatory's Shadow"; VOY: "Equinox, Part II")
In 2373, Garak suggested that Worf repolarize their runabout's hull to free them from a Jem'Hadar fighter's tractor beam. (DS9: "In Purgatory's Shadow")
In 2375, Tom Paris attempted to polarize the Delta Flyer's hull after it had crash-landed in order to make it easier for the USS Voyager's sensors to find them. (VOY: "Once Upon a Time")
In 2376, Voyager's hull was polarized in order mask their approach towards the errant USS Equinox. (VOY: "Equinox, Part II")